def _validate(self):
if self._decoder is None:
from bdec.decode import Decoder
self._decoder = Decoder(self)
class Entry(object):
"""An entry is an item in a protocol that can be decoded.
This class designed to be derived by other classes (not instantiated
directly).
"""
def __init__(self, name, length, children, constraints=[]):
"""Construct an Entry instance.
children -- A list of Entry or Child instances.
length -- Optionally specify the size in bits of the entry. Must be an
instance of bdec.expression.Expression or an integer.
constraints -- A list of constraints for the value of this entry.
"""
if length is not None:
if isinstance(length, int):
length = Constant(length)
assert isinstance(length, Expression)
self.name = name
self.length = length
self._children = ()
self.children = children
self._decoder = None
self._encoder = None
self.constraints = list(constraints)
for constraint in self.constraints:
assert getattr(constraint, 'check') is not None
def _get_children(self):
return self._children
def _set_children(self, children):
from bdec.spec.references import ReferencedEntry
items = []
for child in children:
if isinstance(child, Child):
items.append(child)
else:
items.append(Child(child.name, child))
if isinstance(items[-1].entry, ReferencedEntry):
items[-1].entry.add_parent(items[-1])
self._children = list(items)
children = property(_get_children, _set_children)
def _validate(self):
if self._decoder is None:
from bdec.decode import Decoder
self._decoder = Decoder(self)
def decode(self, data, context={}, name=None):
""" Shortcut to bdec.decode.Decoder(self) """
self._validate()
return self._decoder.decode(data, context, name)
def encode(self, query, value):
if self._encoder is None:
from bdec.encode import create_encoder
self._encoder = create_encoder(self)
value = self._encoder.get_value(query, value, 0, self.name, {})
return self._encoder.encode(query, value, 0, {}, self.name)
def is_hidden(self):
"""Is this a 'hidden' entry."""
return is_hidden(self.name)
def __str__(self):
return "%s '%s'" % (self.__class__.__name__.lower(), self.name)
def __repr__(self):
return "%s '%s'" % (self.__class__, self.name)
def _range(self, ignore_entries):
"""
Can be implemented by derived classes to detect ranges.
"""
return bdec.entry.Range()
def range(self, ignore_entries=set()):
"""Return a Range instance indicating the length of this entry.
ignore_entries -- If self is in ignore_entries, a default Range
instance will be returned. 'self' and all child entries will
be added to ignore_entries.
"""
if self in ignore_entries:
# If an entry is recursive, we cannot predict how long it will be.
return Range()
result = None
if self.length is not None:
try:
min = max = self.length.evaluate({})
result = bdec.entry.Range(min, max)
except UndecodedReferenceError:
pass
if result is None:
ignore_entries.add(self)
result = self._range(ignore_entries)
ignore_entries.remove(self)
return result
